1. Field of the Invention
The present invention relates to systems that use a plurality of electric power generators working together; and more particularly, to systems which operate multiple electric power generators in parallel to provide the power in a more efficient and flexible manner.
2. Description of the Related Art
Standby generators provide electrical power when power is unavailable from an electric utility company (e.g. during weather disturbances) or to provide power at a remote location where utility company power is not available. One type of standby electric generator comprises an internal combustion engine driving an electrical alternator that produces alternating electricity. Other types of standby electric generators include photovoltaic arrays and wind turbine generators.
For electrical systems that require large amounts of power, there can be advantages to employing multiple small generators, rather than a single large generator. In this regard, if one generator fails or requires maintenance, a multi-generator system can still supply some power, whereas a single generator system will not. Further, in a multi-generator system load growth can be accommodated by adding another generator, rather than bearing the cost of replacing a single very large generator with an even larger one.
Furthermore, large generators present difficulties in shipping and installation complexity. Thus by using several smaller generators one can distribute the overall generator weight over a broader area, avoiding the need for special strengthening of the supporting area (e.g. of a roof). Moreover, some smaller generators require less frequent maintenance. A variety of generator systems with multiple generator sets have been described previously as in U.S. Pat. Nos. 4,136,286, 6,653,821 and 7,656,060.
Nevertheless, when using multiple generators with outputs connected in parallel, there is a need to synchronize the alternating electricity that each device produces. This involves matching phase angles of the alternating output voltage and current from each generator. In addition, the magnitude of the voltage produced by each generator must be identical. Traditional generator paralleling techniques have been quite complex, often requiring several additional pieces of equipment to achieve the needed functions. This may include separate synchronizers, load managers, and/or switch gear. Moreover, prior art paralleling systems can require significant time to synchronize the operation of the multiple generators once a power need is appreciated.
In addition, traditional systems are not well suited to mix the power from different types of energy sources (e.g. single-phase generators with three-phase generators), or to address mechanical and electrical load differences, or to address differences in optimal generator usage based on noise, fuel and other requirements at particular times during the day.
One company has noted that conventional two-generator paralleling systems often have as many as fourteen controllers to manage speed, load sharing, synchronization, voltage regulation, the internal combustion engine, and load protection. They then proposed to reduce the number of controllers by creating an integrated digital control, an integrated paralleling switch, and an integrated master control that are linked by a communication bus to the individual generators. This system, however, still requires additional control equipment beyond the controllers in each generator, adding cost and complexity to the overall system.
Hence, there is a need for improvements in the design of systems for paralleling and operating multi-generator systems.